BACKGROUND
This study examined whether higher milk intake before weaning improves growth, immune competence, and metabolic status in dairy calves. The authors note that Australian dairy calf outcomes remain poorer than industry targets, with morbidity of 23.8% against a target of <10% and mortality of 5.6% against a target of <3%. Standard recommendations have historically limited milk to approximately 10% of birth bodyweight daily to encourage concentrate intake and earlier weaning, but newer work suggests this may inadequately support calf development. Because early-life nutrition can shape physiologic systems, the investigators tested whether a higher preweaning milk allowance would improve bodyweight gain and biologic responses to an immune challenge.
METHODS
The experiment followed 20 spring-born Holstein-Friesian heifer calves from birth to 10 weeks of age at the Agriculture Victoria Dairy Research Centre, Ellinbank, Victoria, Australia, from July–October 2020. Calves were randomly assigned at birth to receive either 4 L/day of milk (Low) or 8 L/day of milk (High), with treatment groups balanced for birth weight and estimated Balance Performance Index. All calves were separated from the dam and tube fed 4 L of pooled colostrum within 8 h of birth, followed by a second 2 L colostrum feed 12 h later. Passive transfer was screened at 24–48 h and confirmed by serum IgG; all calves achieved IgG above 10,000 μg/mL. After the first four milk feeds of transition colostrum milk, calves received whole milk twice daily. High-fed calves were stepped up by 2 L/day until reaching full allocation after 2 days. All calves had ad libitum access to lucerne hay and a commercial calf concentrate, with individual feed intake measured by automatic feeders. Mean whole-milk composition during the preweaning period was 3.6 ± 0.58% fat, 3.2 ± 0.16% protein, and 4.9 ± 0.09% lactose. At 42 days of age, calves underwent an immune challenge using a commercial Bovine Respiratory Disease vaccine (Bovilis MH + IBR). Blood samples were collected at birth, day 42, day 50, and day 52. Outcomes included bodyweight, feed intake, white cell count (WCC) and differential, infectious bovine rhinotracheitis (IBR) antibody titres, beta-hydroxybutyrate (BHB), non-esterified fatty acid (NEFA), glucose, insulin, and delayed-type hypersensitivity skin-fold responses. Weekly bodyweight, nutrient intakes, and biomarkers were analyzed using linear mixed models with calf as the unit of analysis and birth body weight and estimated BPI fitted as covariates.
KEY RESULTS
Birth weight did not differ between groups. From 2 weeks of age onward, High calves were significantly heavier than Low calves (p-value < 0.05). By 10 weeks of age, mean bodyweight was 96.7 kg in the High group versus 77.7 kg in the Low group, a difference of 19.0 kg. Average daily gain from birth was 0.83 kg/day in High calves and 0.56 kg/day in Low calves. By design, milk intake was higher in the High group. Low calves consumed the full 4 L/day offered except in the first week, when intake averaged 3.9 L/day. High calves consumed 5.4 ± 0.1 L/day in week 1, 7.6 ± 0.2 L/day in week2, and 7.9 ± 0.1 L/day from two weeks of age onward. Over the whole experiment, Low calves consumed 279 L of milk, containing 61.5 MJ of ME and 71.6 kg of crude protein, whereas High calves consumed 533 L, containing 117.3 MJ of ME and 136.5 kg CP.
Solid feed intake was largely similar between treatments. Concentrate intake did not differ significantly during the study. Total concentrate intake was 25.3 kg DM in the Low group versus 22.5 kg DM in the High group. Hay intake differed only at 7 weeks (p-value = 0.034) and 8 weeks (p-value = 0.033), when it was higher in Low calves. Total hay intake was 10.9 kg DM in the Low group and 7.8 kg DM in the High group.
Immune biomarker differences were most evident after vaccination. Before vaccination, WCC was 7.3 in Low calves and 7.7 in High calves (p-value = 0.574), and neutrophils were 2.6 versus 3.8 (p-value = 0.081). Ten days post-vaccination, WCC was significantly higher in High calves at 11.9 compared with 9.3 in Low calves (p-value = 0.048). Neutrophils were 7.6 in High calves versus 5.2 in Low calves, showing a trend toward significance (p-value = 0.054). IBR titre did not differ before vaccination, at 8 days post-vaccination, or at 10 days post-vaccination: pre-vaccination 17.0 versus 12.6 (p-value = 0.593), 8 days post-vaccination 18.5 versus 14.5 (p-value = 0.642), and 10 days post-vaccination 18.6 versus 16.2 (p-value = 0.785), for Low and High groups respectively. Delayed-type hypersensitivity also did not differ. At 24 h, corrected skin fold increase was 5.9 mm in Low calves and 5.4 mm in High calves (SED = 0.36; p-value = 0.175). At 48 h, corrected increase was 6.2 mm versus 6.6 mm (SED = 0.63; p-value = 0.627).
Metabolic markers favored the High group. At birth, BHB, NEFA, glucose, and insulin did not differ significantly. Pre-vaccination, BHB was lower in High calves at 0.02 compared with 0.07 in Low calves (p-value < 0.001). Ten days post-vaccination, BHB remained lower in High calves at 0.06 versus 0.11 (p-value = 0.012). NEFA did not differ at any time point: for example, 10 days post-vaccination NEFA was 0.20 in Low calves and 0.15 in High calves (p-value = 0.095). Ten days post-vaccination, glucose was higher in High calves at 6.72 compared with 5.46 in Low calves (p-value < 0.001). Insulin was also higher in High calves at 40.18 µIU/mL versus 11.08 µIU/mL, with loge insulin 3.54 versus 2.25 (p-value < 0.001).
CLINICAL IMPLICATIONS
Although this was an animal production study rather than a human clinical trial, the findings have clear veterinary and herd-management relevance. Feeding 8 L/day rather than 4 L/day before weaning improved growth without materially reducing concentrate intake, and it was associated with stronger post-vaccination leukocyte responses and a more favorable metabolic profile. The results do not support routine restricted milk feeding and instead suggest that higher milk allowances during the preweaning phase may improve calf resilience, welfare, and future productivity. The authors also emphasize that larger studies are needed to confirm whether these biologic advantages translate into lower morbidity and mortality and better long-term milk production.